Among the approximately 250,000 spinal cord injured (SCI) in the United States, there is a considerable population of chronic incomplete spinal cord injuries (ISCI) who are designated as ASIA B (some sensory sparing and abolished motor power) or C (some sensory sparing and sub-functional motor power) in the lower extremities. Generally, they are wheelchair-dependent, although they may be able to stand or even take a few crude steps for exercise, but are not consistent functional ambulators at home or within the community.
Two novel strategies have been individually employed to augment locomotion rhythm generation, making use of the adaptability and capacity for retraining/learning of spinal cord circuits: partial weight bearing therapy (PWBT) and epidural spinal cord stimulation (ESCS). PWBT has evolved from observations of chronic spinal animals, whereby moving a treadmill can initiate and sustain locomotion when the body is supported. (See Muir GD, Steeves JD, “Sensorimotor Stimulation to Improve Locomotor Recovery After Spinal Cord Injury”, TINS 1997 ,volume 20, pages 72–77.) As a consequence, various afferent inputs into the intrinsic spinal circuitry contribute to a coordinated locomotion pattern with state-dependent and phase-dependent reflexes. It is well respected that PWBT facilitates functional walking among chronic ASIA D (significant functional motor power) patients. To our knowledge, there are no publications documenting the effect of PWBT among ASIA B and ASIA C patients with regard to transitioning treadmill walking to restoration of functional ambulation in terms of household or community walking.
Non-patterned ESCS, which modulates segmental spinal and/or brain stem-spinal pathways in the ISCI, has also shown potential in initiating and sustaining locomotion among Multiple Sclerosis and ASIA D patients. ESCS at the lumbar enlargement in animals, with low frequency, long pulse duration, and supramotor threshold current intensity, induces hind-limb locomotion patterns following an acute mid-thoracic spinal cord transection. (See Iwahara T, Atsuta Y, Garcia-Rill E, Skinner RD, “Spinal Cord Stimulation-Induced Locomotion in the Adult Cat”, Brain Res Bull 1992, pages 99–105.) These parameters, however, contrast with Dimitrijevic's observations in acute human experiments with clinically complete SCI in a supine position. (See Dimitrijevic MR, Gerasimenko Y, Pinter MM, “Evidence for a Spinal Central Pattern Generator in Humans”, Ann N Y Acad Sci 1998; volume 860: pages 360–376.)
A need presently exists for a method for restoring functional ambulation in individuals having incomplete spinal cord injuries so that these individuals can achieve functional non-assisted walking in their households and communities.